Neutral to ground voltage

[dbabn7]

Good evening:

I was watching a mike holt video and he mentioned that in building that has power, if we test neutral to ground we will get some voltage, which that will be the voltage drop of the feeder neutral. Does anyone have any references on this subject? How is there voltage if the ground wire and neutral are connected at the main bonding jumper how is there a difference of potential? any tips on understanding this? Thank you

 

[LarryFine]

How is there voltage if the ground wire and neutral are connected at the main bonding jumper how is there a difference of potential?

Because the measurements he's referring to are made at points downstream in the system, such as along feeders to sub-panels.

Imagine a voltmeter with really long test leads, and you measured for voltage between ends of the same conductor. From the bonding point at the service to the farthest point of a loaded feeder.

As you would expect, there would be no voltage from the service neutral to the far end of the EGC. However, there would be voltage between the service neutral and the other end of the neutral.

Thus, any voltage drop along the feeder neutral would be represented as voltage between the sub-panel's neutral and the EGC.

That is, unless the feeder just happened to be evenly loaded between or among phases, in which case there would be no current-caused voltage drop on the feeder neutral.

 

[ptonsparky]

How can there be an elevated voltage of a feeder or branch circuit neutral to bonded building steel?

See Post #2.

 

[mopowr steve]

I’ve wondered why this has now been allowed, as back in the 90’s we were told that electronics/computers/etc did not like anything over 3 volts between neutral and egc.

 

[Strathead]

I’ve wondered why this has now been allowed, as back in the 90’s we were told that electronics/computers/etc did not like anything over 3 volts between neutral and egc.

That is why they ran an isolated ground for those systems.

 

[ptonsparky]

Data transmission is different. Power supplies are different.

 

[Dsg319]

Good evening:

I was watching a mike holt video and he mentioned that in building that has power, if we test neutral to ground we will get some voltage, which that will be the voltage drop of the feeder neutral. Does anyone have any references on this subject? How is there voltage if the ground wire and neutral are connected at the main bonding jumper how is there a difference of potential? any tips on understanding this? Thank you

They have a slight difference in potential because of the voltage drop along the length of the neutral conductor.

The longer the conductors the more physical resistance there is. Causing more voltage drop among the circuit. Say you have simple 2 wire circuit and a total of 4 volts drop along a circuit. And your checking at the load end and instead if seeing 120v (like you see in your main panel) you see 116v.

You than should see 2v between hot and egc. And 2v between neutral and egc.

The voltage drop is along the whole length of the conductors proportionally (in theory).

So say you check the (isolated) neutral in a garage sub panel to the egc you are just seeing the voltage drop among the feeder circuit. And that will fluctuate as the loads change.

Make an experiment with it and draw the circuit out and will help you be able to visualize it all.

 

[ptonsparky]

" ..2v between hot and egc."
??

 

[Dsg319]

" ..2v between hot and egc."
??

Sorry it early lol. 118v

 

[Speedskater]

I’ve wondered why this has now been allowed, as back in the 90’s we were told that electronics/computers/etc did not like anything over 3 volts between neutral and egc.

That voltage drop was caused by high current flow in the Neutral. The EGC should have zero drop, but real world leakage and noise currents will cause a few millvolts drop.

 

[dbabn7]

They have a slight difference in potential because of the voltage drop along the length of the neutral conductor.

The longer the conductors the more physical resistance there is. Causing more voltage drop among the circuit. Say you have simple 2 wire circuit and a total of 4 volts drop along a circuit. And your checking at the load end and instead if seeing 120v (like you see in your main panel) you see 116v.

You than should see 2v between hot and egc. And 2v between neutral and egc.

The voltage drop is along the whole length of the conductors proportionally (in theory).

So say you check the (isolated) neutral in a garage sub panel to the egc you are just seeing the voltage drop among the feeder circuit. And that will fluctuate as the loads change.

Make an experiment with it and draw the circuit out and will help you be able to visualize it all.

Thank you very much for sharing your knowledge

 

[dbabn7]

They have a slight difference in potential because of the voltage drop along the length of the neutral conductor.

The longer the conductors the more physical resistance there is. Causing more voltage drop among the circuit. Say you have simple 2 wire circuit and a total of 4 volts drop along a circuit. And your checking at the load end and instead if seeing 120v (like you see in your main panel) you see 116v.

You than should see 2v between hot and egc. And 2v between neutral and egc.

The voltage drop is along the whole length of the conductors proportionally (in theory).

So say you check the (isolated) neutral in a garage sub panel to the egc you are just seeing the voltage drop among the feeder circuit. And that will fluctuate as the loads change.

Make an experiment with it and draw the circuit out and will help you be able to visualize it all.

I really appreciate your response, thank you very much.

 

[jaggedben]

I’ve wondered why this has now been allowed, as back in the 90’s we were told that electronics/computers/etc did not like anything over 3 volts between neutral and egc.

It's always been allowed. AFAIK the NEC has never had more than an informational note about voltage drop. No requirements. Besides, an acceptable level depends on the application.

 

[don_resqcapt19]

Part of this neutral to earth voltage comes from the voltage drop on the utility primary neutral in areas where the distribution transformers are connected line to neutral on the primary side.
Remember that when you connect something to earth where that something has a voltage on it, you don't take the voltage away from that something...you just energize a small part of the earth to that voltage.

 

[mtnelect]

Good evening:

I was watching a mike holt video and he mentioned that in building that has power, if we test neutral to ground we will get some voltage, which that will be the voltage drop of the feeder neutral. Does anyone have any references on this subject? How is there voltage if the ground wire and neutral are connected at the main bonding jumper how is there a difference of potential? any tips on understanding this? Thank you

This is what get, because the utilities wanted to save money ... The neutral at the pole should have been insulated from the start as a separated conductor and not combined with the triplex guy wire.

 

[retirede]

This is what get, because the utilities wanted to save money ... The neutral at the pole should have been insulated from the start as a separated conductor and not combined with the triplex guy wire.

Any point in the system that is any distance from where the N-G is bonded will show some voltage differential. A separated N-G from the utility transformer would provide no tangible benefit.

 

[kwired]

Because quite often the "grounded conductor" is bonded to a primary side "grounded conductor" some the measured voltage OP mentioned is actually voltage drop in the primary grounded conductor.

If you have no load, service disconnect off, even disconnect the service neutral and still measure a small voltage to earth, the reading you have is from VD on whatever is ahead of your service, if there is no other services on the secondary voltage source, then it has to be coming from VD on the primary grounded conductor.

 

[ptonsparky]

Most of our tool pouch testers won't be good enough for these low measurements, but then again they don't mean much for most checks.

 

[mtnelect]

This is where I got my information.